This project is based upon the premise that the homeostasis of Ca2+ ion concentrations in neuronal tissue may be perturbed in old-age, and that this perturbation may underlie the decreased production and release of the neurotransmitter acetylcholine which has been described in old age. We have further suggested that a decreased activation by the calcium ion of the enzyme pyruvate dehydrogenase may occur upon depolarization of nerve- terminals from aged animal, and that this may be responsible for decreased production of acetyl-CoA, and thence acetylcholine. Using rat synaptosomes (pinched-off presynaptic nerve endings from cerebral cortex) as a model, we have shown that the synthesis and release of acetylcholine as measured using radiolabelled precursors is indeed decreased in old-age. However, we have this year failed to establish any difference in the degree of activation of pyruvate dehydrogenase upon plasma-membrane depolarization when synaptosomes from 24 month old rats are compared with those from 6 month old animals. In view of the heterogeneity of synaptosomal preparations, and the strong possibility that the age-linked decrement in acetylcholine synthesis and release may only reflect the behavior of a sub- population of synaptosomes, we would regard our experimental results as preliminary results which fail to support the hypothesis outlined above, rather than as requiring the rejection of the hypothesis.